1. Field of the Invention
This invention relates to a method and an apparatus for producing glossy printed matter. More particularly, it relates to such a method and apparatus wherein a web-fed printing paper or printed matter is coated with a coating agent for roll press working and subject to hot roll press working while in the state of a web.
2. Description of Prior Art
High gloss and resistance are freqeuntly required of printed matter from the viewpoints of high quality and finely decorative appearance.
For example, when printed matter is employed for a packaging container, such as a carton for a gift, there is a need to accentuate the impression that the contents, such as an electrical appliance or detergent, are of high quality. The printed matter used for this purpose is therefore required to possess a high degree of gloss, rub-resistance, water-resistance and resistance to contamination. The same characteristics are also required of posters, calendars, the cover pages of books and shopping bags.
Heretofore, in producing printed matter having a high gloss, papers having excellent smoothness, such as a cast-coated paper, have been employed. Such a cast-coated paper is obtained by coating paper supplied by a paper manufacturer, with a coating agent containing a large amount of clay, and contacting the coated layer with the cast surface of a drum plated with chromium. Since this cast-coated paper contains a large amount of clay, it is heavy and hard, lacking in folding endurance. Moreover, it has poor water resistance and inferior rub-resistance, because it is intended to be employed in printing following the casting operation.
Consequently, the gloss-bearing surface of the cast-coated paper itself is effective in the printing, but the gloss of the printed area is thereby lowered and said resistances of the finished printed matter are insufficient. In order to obtain higher resistance, it is necessary to perform a post-processing, such as over-varnishing. This however, leads to a loss of cost-effectiveness because of the cost of the cast-coated paper itself and the necessity to perform post-processing.
Consequently, it is necessary to provide a coating of so-called over-varnishes or laminating a plastic film over the printed matter, this being the conventional means of providing gloss for the printed product.
The method of applying over-varnishes, while being effective to a limited extent in improving the gloss, is not able to fully meet the high demand in the market for glossy products of high quality and a finely decorative appearance.
The so-called UV curable over-varnishes, in which UV rays are employed as the drying means, exhibits excellent gloss characteristics but is unsatisfactory in providing a mirror surface finish and assumes a hard film upon curing, as well as low folding endurance. Moreover, this method presents problems in cost terms since a special drying device is necessitated and the UV varnish itself is expensive.
In regard to the latter method, although a high gloss may be obtained due to the use of the plastic film, the final product lacks satisfactory transparency due to non-uniform coating of the adhesive employed in bonding the film to the paper, so its quality is poor. This method is also unsatisfactory from the equipment and cost viewpoints.
Another known technique is to apply a resin solution on the printed matter and to apply, after drying, a direct pressure press or an endless pressure press using stainless belt (so-called endless press) with the aid of a mirror surface of the belt. A high gloss can be obtained by the technique since the resin film which is dried after application is heat-melted and smoothed by the mirror surface, but the direct presssure press method does not lend itself to high productivity because the press working has to be performed individually for each sheet. While the endless press method offers improved productivity as compared with the direct pressure press method because it is formed of endless belt of, for example, stainless steel, and is adapted to allow continuous insertion of printed sheets, one by one, the latter needs to be peeled manually off the belt surface, because the peeling or release action is based on the stiffness of the sheet itself. This method cannot be employed with sheets having a weight of up to 100 g/m.sup.2, since the peeling or release action cannot then be achieved smoothly, even when the paper sheet itself is endowed with a certain degree of stiffness.
In the field of corrugated boards, the demand for high quality or finely decorative products is increasing, and the corrugated boards having high gloss is rapidly rising. In producing corrugated boards having high gloss, an over-coating agent is applied at the stage of, for example, the last printing unit of the printing press in a corrugated board printer or alternatively the printed corrugated boards are coated with vinyl resin solution to impart a final gloss to the finished boards. This method of applying over-varnishes, while being effective to a limited extent in improving the gloss, however, is not able to fully meet the high demand in the market for glossy products. On the other hand, above said press working method cannot be applied to corrugated boards obtained after bonding front and back liners and a core liner, since there would be a risk of the corrugations collapsing due to the pressure. Therefore, if a corrugated board having such high gloss is to be obtained, it is necessary to initially produce a press worked printed sheet, and after then, to bond it a corrugated board. This necessitates a special bonding machine, and productivity is extremely low because the sheets need to be bonded one by one after being brought into registration with each other.